A modern wireless communication network, such as a 3rd or 4th generation wireless network, combines a radio access network (RAN) with an Internet Protocol (IP) network. The RAN supports wireless connectivity over the airlink with a user's mobile station (MS), whereas the IP network provides the MS with access to IP services. For example, FIG. 1 illustrates a wireless communication network 100 based on the Evolved 3rd Generation Partnership Program (3GPP) Packet Switching Domain.
The wireless network 100 involves a radio access technology that enables an MS 10 to access an IP network 102 over an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 12. A base station called an Evolved Node B (eNB) 14 may serve as a hub for radio communications over the E-UTRAN 12. One or more eNBs 14 may be provided in the E-UTRAN 12 for supporting all sub-layers of an airlink protocol carried out for transmitting and/or receiving data packets to and/or from the MS 12.
A service access entity gateway (SAE GW) 16 terminates the MS interface towards the E-UTRAN 12. The SAE GW 16 performs packet routing and forwarding, provides lawful interception of the MS traffic, serves as a local mobility anchoring point for supporting handover between the eNBs 14, and relays traffic between the E-UTRAN 12 and the IP network 102. The network 100 also includes a Mobility Management Entity (MME) 18 for performing mobility management functions such as MS authentication, keeping track of its current location, paging and roaming.
A Packet Data Network Gateway (PDN GW) 20 is provided between the IP network 102 and the SAE GW 16. The PDN GW 20 supports an interface to the IP network 200. In particular, the PDN GW 20 allocates an IP address to the MS 10, provides IP access policy enforcement, performs lawful interception of the IP traffic, supports billing and charging for IP services, and provides per-user based packet filtering.
Based on the coverage provided by the E-UTRAN 12, the network 100 may support MS communications in a limited area. When the MS 10 initiates an active call in the network 100, and then moves to an area which is not covered by the network 100, the initiated call has to be transferred to another network that may use another radio access technology. When the call is transferred to another network, the context relating to the active call, such as quality of service (QoS) context, security associations, compression context, link layer context (e.g. Point-to-Point Protocol), billing and charging information, and multicast session related information, is required to be transferred.
In addition, if the MS 10 is not capable of keeping both radio access technologies active at the same time, it needs to setup new radio access resources and link layer related information using the new radio access mechanism.
In existing IP-based wireless networks, when transitioning between network technologies, the call handover latency is unacceptably high for real-time traffic applications such as Voice over IP (VoIP) or streaming video. Due to the high call handover latency, a user may experience a large break in a video or a voice conversation, or a call may be dropped.
Therefore, there is a need for a handover mechanism that would minimize the handover latency to enable the MS to move seamlessly between networks with different radio access technologies.